The goal of this protocol is to determine the role of streptococcal infection in the pathogenesis of guttate psoriasis. Streptococci isolated from patients with guttate psoriasis are characterized for their exotoxin production. Peripheral blood T cells and skin infiltrates of psoriatic patients are analyzed for superantigenic effects by analysizing them for evidence of selective usage of T cell receptor (TCR) VB genes and correlating TCR gene usage with the streptococcal exotoxin secreted in their pharynx. Streptococcal pyrogenic exotoxins (SPES) are also tested for their capacity to induce psoriasis directly by patch testing nonlesional skin of patients with psoriasis and normal controls with SPES and determine whether these patch test sites develop psoriatic skin lesions.